Circulation paths for fluid dispensing devices

ABSTRACT

In some examples, a fluid system includes a support structure to attach a fluid dispensing device comprising a fluid chamber to contain a fluid, and an orifice to dispense the fluid from the fluid chamber. The fluid system includes a circulation path comprising a path portion in the fluid dispensing device, the circulation path to circulate a fluid flow through the fluid chamber to remove, from the fluid chamber, a particle ingested through the orifice. A filter in the circulation path is to remove the particle from the circulation path.

BACKGROUND

Additive manufacturing machines produce three-dimensional (3D) objectsby building up layers of material. A type of an additive manufacturingmachine is referred to as a 3D printing system. Additive manufacturingmachines are able to receive as input a computer aided design (CAD)model or other digital representation of a physical 3D object to beformed, and build, based on the CAD model, the physical 3D object. Themodel may be processed into layers by the additive manufacturingmachine, and each layer defines a corresponding part (or parts) of the3D object.

BRIEF DESCRIPTION OF THE DRAWINGS

Some implementations of the present disclosure are described withrespect to the following figures.

FIG. 1 is a block diagram of an additive manufacturing machine,according to some examples.

FIG. 2 is a perspective view of a portion of a fluid dispensing device,in accordance with some examples.

FIG. 3 is an enlarged view of a portion of the fluid dispensing device,according to some examples.

FIG. 4 is a bottom view of an interposer layer according to someexamples.

FIG. 5 is a block diagram of a fluid system according to some examples.

FIG. 6 is a block diagram of an additive manufacturing machine accordingto further examples.

FIG. 7 is a flow diagram of a process according to some examples.

Throughout the drawings, identical reference numbers designate similar,but not necessarily identical, elements. The figures are not necessarilyto scale, and the size of some parts may be exaggerated to more clearlyillustrate the example shown. Moreover, the drawings provide examplesand/or implementations consistent with the description; however, thedescription is not limited to the examples and/or implementationsprovided in the drawings.

DETAILED DESCRIPTION

In the present disclosure, use of the term “a,” “an”, or “the” isintended to include the plural forms as well, unless the context clearlyindicates otherwise. Also, the term “includes,” “including,”“comprises,” “comprising,” “have,” or “having” when used in thisdisclosure specifies the presence of the stated elements, but do notpreclude the presence or addition of other elements.

An additive manufacturing machine such as a three-dimensional (3D)printing system can build 3D objects by forming successive layers ofbuild material and processing each layer of build material on a buildplatform. In some examples, a build material can include a powderedbuild material that is composed of particles in the form of fine powderor granules. The powdered build material can include metal particles,plastic particles, polymer particles, ceramic particles, or particles ofother powder-like materials. In some examples, a build material powdermay be formed from, or may include, short fibers that may, for example,have been cut into short lengths from long strands or threads ofmaterial.

In some examples, as part of the processing of each layer of buildmaterial, liquid agents can be dispensed (such as through a printhead oranother fluid dispensing device) to the layer of build material.Examples of liquid agents include a fusing agent (which is a form of anenergy absorbing agent) that absorbs heat energy emitted from an energysource used in the additive manufacturing process. For example, after alayer of build material is deposited onto a build platform (or onto apreviously formed layer of build material) in the additive manufacturingmachine, a fusing agent with a target pattern can be deposited on thelayer of build material. The target pattern can be based on an objectmodel (or more generally, a digital representation) of the physical 3Dobject that is to be built by the additive manufacturing machine.

According to an example, a fusing agent may be an ink-type formulationincluding carbon black, such as, for example, the fusing agentformulation commercially referred to as the V1Q60A “HP fusing agent”available from HP Inc. In an example, a fusing agent may additionallyinclude an infrared light absorber, a near infrared light absorber, avisible light absorber, or an ultraviolet (UV) light absorber. Fusingagents can also refer to a chemical binding agent, such as used in a 3Dprinting system that forms objects using a metal or other type of buildmaterial. In further examples, other types of additive manufacturingagents can be added to a layer of build material.

Following the application of the fusing or binding agent, an energysource (e.g., including a heating lamp or multiple heating lamps thatemit(s) energy) is activated to sinter, melt, fuse, bind, or otherwisecoalesce the powder of the layer of build material underneath the fusingor binding agent. The patterned build material layer (i.e., portions ofthe layer on which the fusing or binding agent was deposited) cansolidify, for example after cooling, and form a part, or across-section, of the physical 3D object.

Next, a new layer of powder is deposited on top of the previously formedlayer, and the process is re-iterated in the next additive manufacturingcycle to form 3D parts in the successive layers of build material. The3D parts collectively form a 3D object (or multiple 3D objects) that isthe target of the build operation.

In other examples, an additive manufacturing machine can be used as partof a sintering process. In the sintering process, as each layer of buildmaterial is deposited, a binder (which is another type of liquid agent)is applied by a printhead or other fluid dispensing device to the layerof build material. Portions of the build material where the binder isapplied are bound together by the binder. The binder can include anultraviolet-curable binder, heat-curable binder, and so forth. After thelayers of build material have been deposited and the binder applied tolocations of each layer of build material, curing of the binder producesa so-called “green part.” The green part is de-powdered to remove anyunbound build material powder. Afterwards, the green part can betransferred to an oven, where the bound build material powder (e.g.,metal particles, etc.) are sintered together to form a highly dense 3Dobject.

A fluid dispensing device includes nozzles to dispense a liquid agent toa layer of build material. In some examples, the fluid dispensing devicecan be mounted to a moveable carriage in the additive manufacturingmachine. During a build process, the carriage can move back and forthalong a scan axis, or multiple scan axes, to deliver liquid agents tothe layer of build material.

A rapid movement of the carriage can result in turbulence that may causepowder on the layer of build material to rise towards the fluiddispensing device, such as in a cloud of powder. In addition, whenliquid agent droplets dispensed from the fluid dispensing device hit thelayer of build material, the impact can cause power particles to lift upfrom the layer of build material. The fine particles of the powder canbe ingested through orifices of the nozzles of the fluid dispensingdevice.

Inside the fluid dispensing device, the particles can travel through theorifices and into respective fluid chambers in fluid communication withthe orifices. A fluid chamber contains a fluid to be dispensed throughthe orifice of the fluid dispensing device.

In some examples, a fluid dispensing device may include a particletolerant architecture (PTA) that includes pillars (or more generally,obstacles) between fluid chambers and a backside channel in the fluiddispensing device. The backside channel transports a fluid that is to befed to the fluid chambers of the fluid dispensing device. There can be apillar (or multiple pillars) between each fluid chamber and the backsidechannel. The pillars are arranged to prevent fibers or othercontaminants that may be present in the fluid contained in the backsidechannel from being delivered to the fluid chambers. This prevents thecontaminants from being dispensed outwardly through the orifices of thefluid dispensing device onto a layer of build material.

However, the presence of the pillars can cause particles ingestedthrough the orifices of the fluid dispensing device to be trapped at thepillars, which can cause blockage of fluid chambers where the particlesare trapped. If a fluid chamber is blocked, then fluid dispensingoperation through the corresponding orifice of the fluid dispensingdevice may be disrupted.

In accordance with some examples of the present disclosure, theobstacles (e.g., pillars) between the fluid chambers of a fluiddispensing device and a backside channel of the fluid dispensing deviceare removed to provide a non-PTA arrangement. Without the obstacles, anyparticles (such as powder particles of an additive manufacturingmachine) ingested through an orifice of the fluid dispensing device canbe allowed to pass through the corresponding fluid chamber and to thebackside channel. To allow for removal of particles that have beeningested into fluid chambers through corresponding orifices, a fluidcirculation path is provided to circulate fluid flow through the fluidchambers. The circulated fluid flow is able to transport any particlesaway from the fluid chambers through the backside channel and out of thefluid dispensing device.

In accordance with some implementations of the present disclosure, afilter is provided in the circulation path to remove particles that arecarried in the circulated fluid flow.

FIG. 1 shows an example additive manufacturing machine 100, which insome examples can include a 3D printer. The additive manufacturingmachine 100 includes a spreader 102 that is used to spread a buildmaterial 104 (in powder form) onto a build bed 106. The build bed 106can either be a base plate (if a first layer of build material is beingdispensed) or a previously formed 3D part (formed using a layer buildmaterial or multiple layers of build material). The spreader 102 can bein the form of a blade, a roller, and so forth.

The spreader 102 is moved along a spreading direction 105 (or multiplespreading locations), starting at a supply station 108 that supplies thebuild material 104. A dispensing surface 110 of the powder supplystation 108 has a supply of build material 104 that is spread by thespreader 102 across the upper surface of the build bed 106 as thespreader 102 is moved in the spreading direction 105 across the buildbed 106. A layer of build material 112 (hereinafter referred to as a“build material layer”) is formed on the build bed 106.

Once the build material layer 112 is formed on the build bed 106, afluid dispensing device 114 (which can include a printhead, for example)can be activated to dispense a liquid agent 116 onto a surface of thebuild material layer 112. The fluid dispensing device 114 can include anarray of nozzles 115 that include respective orifices through whichdrops of the liquid agent can be dispensed towards the build materiallayer 112. In some examples, the fluid dispensing device 114 (ormultiple fluid dispensing devices) can dispense different types ofliquid agents onto the build material layer 112.

The fluid dispensing device 114 (or multiple fluid dispensing devices)can be attached to a carriage 118 or any other type of support structureof the additive manufacturing machine 100. In some examples, the fluiddispensing device 114 is removably attached to the carriage 118. Thus,the additive manufacturing machine 100 can initially be provided withoutthe fluid dispensing device 114, such as during transport of theadditive manufacturing machine 100 from a seller or manufacturer to acustomer or other end user. The end user can then attach the fluiddispensing device 114 to the carriage 118 prior to use of the additivemanufacturing machine 100.

In some examples, the carriage 118 is moveable along a scan axis, ormultiple scan axes. For example, the carriage 118 is moveable along ascan axis X. In other examples, the carriage 118 is moveable alongmultiple scan axes X and Y. The scan axes X and Y are generallyhorizontal in the view of FIG. 1, and extend in a plane that isgenerally perpendicular to the direction of travel of liquid agentsbeing dispensed by the fluid dispensing device 114 toward the buildmaterial layer 112.

Also, in some examples, the carriage 118 may be moveable along avertical axis Z (in the view of FIG. 1) relative to the build bed 106.The vertical axis Z is generally perpendicular to each of the horizontalscan axes X and Y.

In other examples, the carriage 118 can be fixed in place, but the buildbed 106 is moveable relative to the carriage 118 along any or somecombination of axes X, Y, and Z.

In alternative examples, both the carriage 118 and the build bed 106 aremoveable relative to each other.

The additive manufacturing machine 100 includes a fluid delivery system120, which includes a fluid source 122. The fluid source 122 includes areservoir to store a liquid agent that is to be delivered to the fluiddispensing device 114 that is attached to the carriage 118. In someexamples, the fluid source 122 is a pressurized fluid source that cancreate a pressure differential to cause a flow of fluid from the fluidsource 122 to the fluid dispensing device 114. For example, thepressurized fluid source 122 can include a fluid pump that creates thepressure differential.

In other examples, multiple fluid sources 122 can be provided to deliverrespective different liquid agents to the fluid dispensing device 114that is attached to the carriage 118.

In accordance with some implementations of the present disclosure, thefluid source 122 causes fluid to circulate in a circulation path thatincludes a supply circulation path segment 124-S, and a returncirculation path segment 124-R. Fluid is transported from the fluidsource 122 through the supply circulation path segment 124-S to thecarriage 118, and through a fluid channel 126 in the carriage 118 to thefluid dispensing device 114. After flowing through the fluid dispensingdevice 114, the fluid returns from the fluid dispensing device 114through a fluid channel 128 in the carriage 118 and through the returncirculation path segment 124-R to the fluid source 122.

The circulation path for the circulated fluid flow includes the supplycirculation path segment 124-S, the carriage fluid channel 126, fluidchannels in the fluid dispensing deice 114, the carriage fluid channel128, and the return circulation path segment 124-R.

In accordance with some implementations of the present disclosure, anypowder particles (or other types of particles) ingested through theorifices of the nozzles 115 into respective fluid chambers 117 of thefluid dispensing device 114 can be carried by the circulated fluid flowalong the circulation path away from the fluid chambers 117 and backalong the return circulation path segment 124-R.

A filter 130 is provided in the return circulation path segment 124-R toremove any particles contained in the fluid flowing in the returncirculation path segment 124-R. In some examples, the filter 130 cancapture any particles that have a size greater than 0.5 micrometers(μm). In further examples, the filter 130 can capture particles having asize of greater than another threshold size, such as 1 μm, 2 μm, 10 μm,20 μm, 30 μm, 50 μm, 100 μm, and so forth. A “size” of a particle canrefer to a diameter of the particle (assuming the particle is generallyspherical in shape) or any other dimension of the particle, where thedimension represents an extent of the particle from one edge to anotheredge.

Fluid flowing in the return circulation path segment 124-R flows throughthe filter 130, which is able to remove any particles of specified sizesthat flow through the return circulation path segment 124-R.

Although FIG. 1 shows placement of the filter 130 in the returncirculation path segment 124-R, it is noted that in other examples, thefilter 130, or another filter, may be placed in the supply circulationpath segment 124-S. In further examples, multiple filters may beincluded in the fluid delivery system 120.

In some examples, the fluid delivery system 120 can be separate from thecarriage 118. In further examples, the fluid delivery system 120 can bemounted on the carriage 118.

In alternative examples, instead of arranging the filter 130 to beseparate from the carriage 118 the filter 130 can be part of thecarriage 118, and can be placed to remove particles from fluid flowingthrough the channel 126 or 128 in the carriage 118.

In some examples, a sensor 132 can be associated with the filter 130.The sensor 132 can detect a condition of the filter 130. For example,the sensor 132 includes a pressure sensor that detects a pressuregradient across the filter 130, from one side 130-1 of the filter 130the other side 130-2 of the filter 130. An unclogged filter 130 willhave a relatively low pressure gradient across the filter 130 betweenthe sides 130-1 and 130-2. However, as the filter 130 collectsparticles, the filter 130 becomes clogged, which increases the pressuredifferential across the filter 130 between the sides 130-1 and 130-2.

In other examples, other types of sensors can be employed, such assensors for detecting electrical conductivity or resistivity across thefilter 130 between the first side 130-1 and the second side 130-2.

The sensor 132 can send measurement data 134 to a controller 136. Forexample, the measurement data 134 can include pressure data.

As used here, a “controller” can refer to a hardware processing circuit,which can include any or some combination of a microprocessor, a core ofa multi-core microprocessor, a microcontroller, a programmableintegrated circuit, a programmable gate array, a digital signalprocessor, or another hardware processing circuit. Alternatively, a“controller” can refer to a combination of a hardware processing circuitand machine-readable instructions (software and/or firmware) executableon the hardware processing circuit.

The controller 136 determines from the measurement data 134 whether thefilter 130 should be replaced. For example, if the measured pressureacross the filter 130 exceeds a specified threshold, then that indicatesthat the filter 130 is clogged and should be replaced.

If the controller 136 determines from the measurement data 134 that thefilter 130 should be replaced, the controller 136 can issue an alert138. The alert 138 can be in the form of a visual indicator, which caninclude activation of a light indicator on the additive manufacturingmachine 100. Alternatively, the alert 138 can include a message, such asan e-mail message, a text message, or other information sent to a remotecomputing device, such as a desktop computer, a notebook computer, atablet computer, a smartphone, and so forth.

More generally, the controller 136 receives the measurement data 134 ofthe sensor 132, and outputs an indication of a condition of the filter130 in response to the measurement data 134.

FIG. 2 is a perspective view of a portion of the fluid dispensing device114. In some examples, the fluid dispensing device 114 can include afluidic die, such as a printhead die used in printing operations. A“die” refers to an assembly where various layers are formed onto asubstrate to fabricate circuitry, fluid chambers, and fluid conduits.Multiple fluidic dies can be mounted or attached to a support structure.

FIG. 2 shows various layers of a fluidic die that forms part of thefluid dispensing device 114. The fluidic die includes a substrate (notshown) on which various layers are formed. The layers include aninterposer layer 212 and a backside channel layer 210 formed on theinterposer layer 212.

A portion 202 of the fluidic die is shown in an enlarged view of FIG. 3.In the view of FIG. 3, a chamber layer 204 is formed over the backsidechannel layer 210, and an orifice layer 208 is formed over the chamberlayer 204.

The chamber layer 204 defines various fluid chambers 209 (one fluidchamber 209 is shown in FIG. 3). The orifice layer 208 defines variousorifices 211. A fluid (a liquid agent) is delivered to the fluidchambers 209, and upon activation of a fluidic actuator (not shown), thefluid in the respective fluid chamber 209 is ejected through thecorresponding orifice 211.

In some examples, each of the chamber layer 204 and the orifice layer208 can be formed using an epoxy or another material.

In some examples, fluidic actuators include thermal-based fluidicactuators including heating elements, such as resistive heaters. When aheating element is activated, the heating element produces heat that cancause vaporization of a fluid to cause nucleation of a vapor bubble(e.g., a steam bubble) proximate the thermal-based fluidic actuator thatin turn causes dispensing of a quantity of fluid, such as ejection froman orifice of a nozzle or flow through a fluid conduit or fluid chamber.In other examples, a fluidic actuator may be a piezoelectric membranebased fluidic actuator that when activated applies a mechanical force todispense a quantity of fluid.

The substrate includes an interposer layer 212. An inlet 214 and anoutlet 216 are formed in the interposer layer 212. The inlet 214 carriesfluid (part of a fluid flow 215-1) received from the supply circulationpath segment 124-S and provides the fluid to an inlet backside channel218-1 in the backside channel layer 220.

The fluid flow 215-1 in the inlet backside channel 218-1 flows from theinlet backside channel 218-1 into an inlet feedhole 224-1 (FIG. 3)formed in the backside channel layer 210, and then into thecorresponding fluid chamber 209. The fluid flow continues through thefluid chamber 209 and exits an outlet feedhole 224-2 (FIG. 3) formed inthe backside channel layer 210, and flows to an outlet backside channel218-2. The fluid (part of a fluid flow 215-2) flows through the outletbackside channel 218-2 and exits the outlet 216 in the interposer layer212, and flows to the return circulation path segment 124-R.

The fluid flows 215-1 and 215-2 are part of the circulated fluid flow inthe circulation path discussed above.

In the view of FIG. 2, a diagonal cut 203 is made in the layers 212,210, 204, and 208 to show the feedholes 224-1 and 224-2, the fluidchamber 209, and an orifice 211 (FIG. 3). Note that the inlet backsidechannel 218-1 and the outlet backside channel 218-2 are at differentsectional depths. The diagonal cut 203 allows both the inlet backsidechannel 218-1 and the outlet backside channel 218-2 to be visible inFIG. 2.

Additionally, in some examples, there are multiple inlet backsidechannels 218-1 and multiple outlet backside channels 218-2.

For each fluid chamber 209, a pair of fluid feedholes 224-1 and 224-2are provided. Fluid is transferred from the inlet backside channel 218-1through the inlet feedholes 224-1 to the corresponding fluid chambers209. The fluid is then passed from the fluid chambers 209 through thecorresponding outlet feedholes 224-2 to the outlet backside channel218-2.

During operation of the additive manufacturing machine 100, circulatedfluid flows from the fluid source 122 through the supply circulationpath segment 124-S to the fluidic die shown in FIG. 2. The circulatedfluid from the supply circulation path segment 124-S is passed throughthe inlet 214 of the interposer layer 212, and into the inlet backsidechannel 218.

The circulated fluid continues to flow from the inlet backside channel218-1 through the inlet feedholes 224-1 to respective fluid chambers209. The circulated fluid continues from the fluid chambers 209 throughthe outlet feedholes 224-2 to the outlet backside channel 218-2. Thecirculated fluid exits the outlet 216 and flows to the returncirculation path segment 124-R.

In this way, any particles that have been ingested through respectiveorifices 211 into corresponding fluid chambers 209 are removed by thecirculated flows away from the fluidic die. The particles carried by thecirculated flow are removed by the filter 130 (FIG. 1).

FIG. 4 is a bottom view of the interposer layer 212 according to furtherexamples. A central portion 402 of the interposer layer 212 has been cutaway to illustrate inlet backside channels 218-1 and outlet backsidechannels 218-2 that are above the interposer layer 212. The inlet andoutlet backside channels 218-1 and 218-2 are formed in the backsidechannel layer 210.

The inlets 214 receive fluid from the supply circulation path segment124-S. The fluid received at the inlets 214 are transferred torespective inlet backside channels 218-1. The fluid in the inletbackside channels 218-1 are transferred through inlet feedholes 224-1 tocorresponding fluid chambers 209. The fluid is then returned from thefluid chambers 209 through the outlet feedholes 224-2 to the outletbackside channels 218-2, and the fluid exits through respective outlets216.

FIG. 5 is a block diagram of a fluid system 500. The fluid system 500can be part of an additive manufacturing machine (e.g., 100 in FIG. 1).The fluid system 500 includes a support structure 501 to attach a fluiddispensing device 502 that has a fluid chamber 504 to contain a fluid,and an orifice 506 to dispense the fluid from the fluid chamber 504.

The support structure 501 can be the carriage 118 of FIG. 1, forexample. The fluid dispensing device 502 may be removably attachable tothe support structure 501, and may not be present until an end userattaches the fluid dispensing device 502 to the support structure 501.

The fluid system 500 further includes a circulation path 508 that has apath portion 510 in the fluid dispensing device 502. The circulationpath 508 circulates a fluid flow through the fluid chamber 504 toremove, from the fluid chamber, a particle ingested through the orifice506.

The fluid system 500 further includes a filter 512 in the circulationpath 508 to remove the particle from the circulation path 508.

In some examples, the fluid system 500 can include a fluid source (e.g.,122 in FIG. 1) to supply a circulation path fluid for the circulationpath 508.

In some examples, the fluid dispensing device 502 includes a fluidic die(e.g., the fluidic die shown in FIGS. 2 and 3).

In some examples, the fluidic die includes a layer (e.g., 212 in FIG. 2)having an inlet (e.g., 214 in FIG. 2) to the fluid chamber 504, and anoutlet (e.g., 216 in FIG. 2) from the fluid chamber 504. The fluid flowtransports a portion of a circulation path fluid through the inlet tothe fluid chamber 504, and transports the first portion of thecirculation path fluid from the fluid chamber 504 through the outlet.

In some examples, the fluidic die further includes a backside channellayer (e.g., 210 in FIG. 2) that has an inlet backside channel (e.g.,218-1 in FIG. 2) to carry the first portion of the circulation pathfluid from the inlet to the fluid chamber 504, and an outlet backsidechannel (e.g., 218-2 in FIG. 2) to carry the first portion of thecirculation path fluid from the fluid chamber to the outlet.

In some examples, the fluid dispensing device 502 is without anyobstacles between the fluid chamber 504 and a backside channel thatfeeds the fluid to the fluid chamber 504.

In some examples, the fluid dispensing device 502 is to dispense thefluid to a powder surface, wherein the particle comprises a powder usedfor the powder surface.

FIG. 6 is a block diagram of an additive manufacturing machine 600according to further examples. The additive manufacturing machine 600includes a support structure 601 to attach a fluid dispensing device 602that has a fluid chamber 604 to contain a fluid, and an orifice 606 todispense the fluid from the fluid chamber 604 to a build bed of theadditive manufacturing machine 600.

The additive manufacturing machine 600 includes a fluid delivery system608 to deliver a fluid from a fluid source 611 to the support structure601. The fluid delivery system 608 includes a circulation path 610 tocirculate the fluid through the fluid chamber 604 to remove, from thefluid chamber 604, a particle ingested through the orifice 606.

The additive manufacturing machine 600 includes a filter 612 in thecirculation path 610 to remove the particle from the circulation path610.

FIG. 7 is a flow diagram of a process according to some examples. Theprocess includes supplying (at 702), through a circulation path, a fluidthrough an inlet to a fluid chamber of a fluid dispensing device, thefluid dispensing device including an orifice to dispense the fluid fromthe fluid chamber.

The process includes transporting (at 704), through the circulationpath, the fluid from the fluid chamber through an outlet to a fluidchannel, the fluid transported from through the outlet to the fluidchannel removing, from the fluid chamber, a particle ingested throughthe orifice.

The process includes flowing (at 706) the fluid through a filter in thecirculation path, the filter removing the particle from the circulationpath.

In the foregoing description, numerous details are set forth to providean understanding of the subject disclosed herein. However,implementations may be practiced without some of these details. Otherimplementations may include modifications and variations from thedetails discussed above. It is intended that the appended claims coversuch modifications and variations.

What is claimed is:
 1. A fluid system comprising: a support structure toattach a fluid dispensing device comprising a fluid chamber to contain afluid, and an orifice to dispense the fluid from the fluid chamber; acirculation path comprising a path portion in the fluid dispensingdevice, the circulation path to circulate a fluid flow through the fluidchamber to remove, from the fluid chamber, a particle ingested throughthe orifice; and a filter in the circulation path to remove the particlefrom the circulation path.
 2. The fluid system of claim 1, furthercomprising a fluid source to supply a circulation path fluid for thecirculation path.
 3. The fluid system of claim 2, wherein thecirculation path comprises: a supply circulation path segment totransport the circulation path fluid from the fluid source to the fluiddispensing device, and a return circulation path segment to transportthe circulation path fluid from the fluid dispensing device to the fluidsource.
 4. The fluid system of claim 3, wherein the filter is arrangedto remove particles in the circulation path fluid flowing in the returncirculation path segment.
 5. The fluid system of claim 1, furthercomprising a sensor to detect a condition of the filter.
 6. The fluidsystem of claim 5, further comprising: a controller to receivemeasurement data of the sensor, and to output an indication of acondition of the filter in response to the measurement data.
 7. Thefluid system of claim 1, wherein the fluid dispensing device comprises afluidic die.
 8. The fluid system of claim 7, wherein the fluidic diecomprises a first layer comprising an inlet to the fluid chamber, and anoutlet from the fluid chamber, and wherein the fluid flow transports afirst portion of a circulation path fluid through the inlet to the fluidchamber, and transports the first portion of the circulation path fluidfrom the fluid chamber through the outlet.
 9. The fluid system of claim8, wherein the fluidic die further comprises a backside channel layercomprising: an inlet backside channel to carry the first portion of thecirculation path fluid from the inlet to the fluid chamber, and anoutlet backside channel to carry the first portion of the circulationpath fluid from the fluid chamber to the outlet.
 10. The fluid system ofclaim 1, wherein the fluid dispensing device is without any obstaclesbetween the fluid chamber and a channel to feed the fluid to the fluidchamber.
 11. The fluid system of claim 1, wherein the fluid dispensingdevice comprises a printhead to dispense a print liquid to a powdersurface, wherein the particle comprises a powder used for the powdersurface.
 12. An additive manufacturing machine comprising: a supportstructure to attach a fluid dispensing device comprising a fluid chamberto contain a fluid, and an orifice to dispense the fluid from the fluidchamber to a build bed of the additive manufacturing machine; a fluiddelivery system to deliver a fluid from a fluid source to the fluiddispensing device, the fluid delivery system comprising a circulationpath to circulate the fluid through the fluid chamber to remove, fromthe fluid chamber, a particle ingested through the orifice; and a filterin the circulation path to remove the particle from the circulationpath.
 13. The additive manufacturing machine of claim 12, furthercomprising a sensor to detect a condition of the filter.
 14. A methodcomprising: supplying, through a circulation path, a fluid through aninlet to a fluid chamber of a fluid dispensing device, the fluiddispensing device comprising an orifice to dispense the fluid from thefluid chamber; transporting, through the circulation path, the fluidfrom the fluid chamber through an outlet to a fluid channel, the fluidtransported from through the outlet to the fluid channel removing, fromthe fluid chamber, a particle ingested through the orifice; and flowingthe fluid through a filter in the circulation path, the filter removingthe particle from the circulation path.
 15. The method of claim 14,wherein the circulation path comprises an inlet backside channel in thefluid dispensing device, and an outlet backside channel in the fluiddispensing device, the inlet backside channel to provide a fluid flow tothe fluid chamber, and the outlet backside channel to receive fluid flowfrom the fluid chamber.